This invention relates to a method of cooling the surface of skin by applying thereto a topical aqueous gel composition containing a starch-polyacrylonitrile graft copolymer.
Skin surface coolants are particularly useful for applying to the surface of skin that has been overheated by excessive exposure to sun and/or wind, although other causes of elevated skin surface temperatures can be treated by the method of this invention.
Although starch-polyacrylonitrile graft copolymers are known to absorb large amounts of water to form gels and have been used in a variety of applications, they have not heretofore been used in topical skin cooling compositions.
Starch-polyacrylonitrile graft copolymers are generally prepared by reacting starch with acrylonitrile as shown in the following U.S. patents.
Smith, U.S. Pat. No. 3,661,815, issued May 9, 1972 discloses a method of preparing starch-acrylonitrile graft copolymers by reacting corn starch with acrylonitrile in the presence of ceric ammonium nitrate. The resulting products have a mole ratio of starch to acrylonitrile of 1:1 to 1:6. They are converted to an alkali metal carboxylate salt by saponifying the starch-acrylonitrile graft copolymer.
This is the method used to produce the preferred copolymer of this invention.
Duchane, U.S. Pat. No. 3,932,322, issued Jan. 13, 1976,discloses improved alkali metal carboxylate salts of starch-acrylonitrile graft copolymers capable of absorbing, before improvement, in excess of 50 parts by weight aqueous fluids per part of copolymer. The mole ratio of acrylonitrile to starch in the copolymers is 2:1 to 10:1. The improvement is mixing in fumed silica or fumed alumina. This results in improved absorption of saline physiological fluids and reduces dusting.
Gugliemelli et al, U.S. Pat. No. 3,984,361, issued Oct. 5, 1976, disclose a stable gelatinized cationic starch graft copolymer latex. The starch is copolymerized with a cationic vinyl monomer, e.g. acrylonitrile.
Weaver et al, U.S. Pat. No. 3,997,484, issued Dec. 14, 1976, discloses aqueous fluid-absorbing compositions of water-insoluble alkali salts of aqueous alkali saponified gelatinized-starch-polyacrylonitrile graft polymers having starch and polyacrylonitrile mole ratios of 1:1.5 to 1:9. The copolymers are capable of absorbing in excess of 300 parts of water by weight.
Smith, U.S. Pat. No. 4,069,177, issued Jan. 17, 1978, discloses alkali metal carboxylate salts of a starch-polyacrylonitrile graft copolymer in which the mole ratio of starch to acrylonitrile is at least 1:6.
Jones et al, U.S. Pat. No. 4,159,260, issued June 26, 1979, discloses hydrolyzed polyacrylonitrile-starch graft copolymers blended with a quaternary ammonium chloride.
Antholz et al, U.S. Pat. No. 4,221,684, issued Sept. 9, 1980, disclose aqueous fluid-absorbing compositions of copolymers of starch and acrylonitrile of weight ratios of 3:1 to 1:3. The compositions are capable of absorbing about 3000 to 10,000 parts of water by weight.
None of the patents disclose compositions containing the copolymers disclosed therein as being useful for cooling the surface of skin.